After Effects is pixelated and can't open the exported video

[2_0clthng]

When I drag video into AE the image instantly becomes pixelated. Its only 1080p footge and Ive edited 4k footage on here just fine; I havent added any effects or done anything to the footage and my fast previews are off. Ive tried resarting the computer and deleting Ae and redownloading it with no effect to the situation. Also I tried just exporting the footge to see if it would come out clear or pixelated, but after exporting it, I get an error saying the file isn't compatible with quicktime player even though it was exported in quicktime format. Im running macOS Catalina V.10.15.3 and AE 17.1.1(which is the most upto date at this time) Has anyone else had this problem or do i need to contact adobe?

[Byron Cortez]

Have you already checked the resolution of the Composition panel? Put it in "Auto" or "Full". Also check that the resolution of the Preview panel is also "Auto" or "Full".

[Rick Gerard]

What kind of footage? We need specifics to say anything more than your footage does not comply with production standards. Catalina is a lot pickier about the codecs used than earlier versions of OSX.